This invention relates to the video display of images and, more particularly, to improvements in modifying the video presentation of images representing data characters and the like.
Whereas the invention is described herein in conjunction with video display systems which may incorporate a host computer and individual terminals, it is to be appreciated that the invention is not limited thereto but may also be employed in a stand alone video display terminal or other apparatus for displaying graphical images wherein it is desirable to provide video modifications thereto.
Video display systems which employ terminals having means for displaying data characters as well as for modifying the video characteristics of the displayed characters are known in the art. Typically such systems have a fixed number of video modifications or "enhancements" that can be made and that such modifications deal with non-dot pattern modifications, such as dot position or dot intensity.
Improvements to such systems are represented by the co-pending United States patent application to R. E. Bakula et al., Ser. No. 829,043, filed on Aug. 30, 1977 now U.S. Pat. No. 4,204,207, and assigned to the same assignee as the present invention. That system discloses a pair of read only memories (ROM), one being used to store dot patterns to form characters, and the other being used to store dot patterns to provide video modifications to the characters to be displayed. Coded data words are supplied for addressing these two memories so that for a particular character certain associated video modifications may be made. The dot pattern video signals obtained from the character memory are modified by dot pattern video signals outputted from the enhancement or modification memory by ORing the two outputs together. This, then, provides a modified dot pattern which is used to form the video image representative of the character to be displayed together with one or more modifications to the dot pattern characteristics of the character. However, the number of video modifications that can be had is limited to the fixed number of dot pattern modifications stored in the enhancement memory, each of which is individually addressable.